Search

The copper ion reduction and oxidation cycle during the cathodic process of gold thiosulfate leaching was studied using a rotating disc electrode and cyclic voltammetry, and the dynamic characteristics of the system were discussed. In a copper ammonium solution, the redox reactions of CuNH342+ were reversible and controlled by substance diffusion. The rotating disc electrode and the reduction method with a constant potential showed that the CuNH32+ generated during the reduction process was easily oxidized by O2 to CuNH342+. In the copper ammonium and thiosulfate system, the reversibility of the redox reactions of CuNH342+ became worse, and the reduction process was still controlled by material diffusion and had a higher diffusion coefficient than that in the copper ammonium solution. However, under this condition, the oxidation reaction of the generated Cu(I) species was complicated. The reduction method with a constant potential showed that the rate‐determining step for the cathodic process was the oxidation step of the Cu(I) species. In addition, some amount of Cu(I) species in solution could not be oxidized in time under the experimental conditions. This part of Cu(I) species may be included during the oxidation decomposition of thiosulfate, thus affecting the dissolution of gold. [ABSTRACT FROM AUTHOR]

Adsorption of the gold–thiosulfate complex ion (Au(S2O3)23-) on silver ferrocyanide (AgFC)-impregnated activated carbon in aqueous solution has been studied in order to find an effectual adsorbent for the thiosulfate extracting gold from ores. This study was performed using AgFC-impregnated activated carbon (AC-Ag-R-FC: AC: activated carbon, Ag: silver nitrate, R: heating, FC: potassium ferrocyanide) and an artificial aqueous solution of Au(S2O3)23-. Gold–thiosulfate complex adsorption kinetics and isotherm studies were carried out at pH = 9.0 on modified materials. It has been also found that the adsorption fits the intraparticle diffusion and Freundlich isotherm well. In order to understand the adsorption mechanism, raw and modified materials were characterized by N2 adsorption–desorption measurements at 77 K, scanning electron microscopy and X-ray photoelectron spectroscopy. The maximum adsorption capability of Au(S2O3)23-on AC-Ag-R-FC is 3.55 kgt−1. Clearly, the extraordinary adsorption capacity of AC for Au(S2O3)23- offers a new approach to address challenging gold–thiosulfate complex separation and could promote the future development of thiosulfate leaching gold process. [ABSTRACT FROM AUTHOR]

The mechanism that tetrathionates retarded gold dissolution during the anodic process of gold thiosulfate leaching was studied with the help of electrochemical and spectroscopic techniques. The results show that the reduction in gold dissolution did not originate from the increase of a passive layer on the surface. When the gold electrode was controlled at 0.25 V, the topography of the gold surface and element composition in the tetrathionate‐supplemented solution is not easily distinguishable from that in the thiosulfate solution. The addition of tetrathionate in the thiosulfate solution reduces gold dissolution. This phenomenon is caused by the decrease in thiosulfate concentration at the gold interface. And the gold interface composition was also changed due to the presence of tetrathionate. [ABSTRACT FROM AUTHOR]

One of the main problems affecting the application of gold thiosulfate leaching is the difficulty in recovering gold from the leaching solution. Our previous studies revealed that when using calcined Mg/Al layered double hydroxides (LDHs), the single adsorption capacity of Au(S 2 O 3 ) 2 3- can reach 7.76 mg/g. In order to further examine the recovery of Au(S 2 O 3 ) 2 3- by various types of LDHs, the divalent metal and trivalent metal ions in LDHs were altered. Also, thiosulfate anions are introduced between the layers of LDHs to reduce the competitive adsorption of thiosulfate ions in the solution. Results show that the calcined LDHs (CLDH) prepared with Cu/Fe-LDHs are the best at adsorbing Au(S 2 O 3 ) 2 3- . Compared with Mg/Al-CLDH, the single adsorption capacity reaches 48.6 mg/g. The pseudo-second-order kinetic model is more suitable for describing the adsorption of Au(S 2 O 3 ) 2 3- by Cu/Fe-CLDH. The adsorption isotherm fitting experiment indicates that the adsorption by Cu/Fe-CLDH of Au(S 2 O 3 ) 2 3- conforms to the Langmuir model. During the process of Cu/Fe-CLDH adsorbing Au(S 2 O 3 ) 2 3- , CLDH restored part of the layered structure, and Au(S 2 O 3 ) 2 3- was inserted between the layers as a counteranion. Furthermore, the reduction of Au(S 2 O 3 ) 2 3- by low-valent iron compounds in the adsorbent promoted the process of Cu/Fe-CLDH adsorbing Au(S 2 O 3 ) 2 3- ., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)